This invention relates generally to irrigation sprinklers of the impact drive type, and, more particularly, to an impact arm for such a sprinkler which is relatively compact in size and is capable of driving the sprinkler in both the forward and reverse directions when operated at relatively low supply pressures.
As is well known in the art, it is highly desirable for a part circle, impact drive sprinkler to be provided with a means by which the stream of water which acts upon the impact arm of the sprinkler is ejected by the impact arm in a direction substantially parallel to the stream of water ejected by the sprinkler nozzle. In this way, undesirable side or back splash from the sprinkler is minimized, and the sprinkler irrigates only the area intended to be irrigated. One highly successful sprinkler intended to solve this problem is that described and claimed in U.S. Pat. No. 3,022,012, which issued on Feb. 20, 1962 to C. R. Sharp et al. Although sprinklers constructed in accordance with the Sharp et al patent operate satisfactorily, for a given size sprinkler and nozzle diameter, there is a minimum water supply pressure above which water must be supplied to that sprinkler in order to achieve satisfactory water distribution and sprinkler operation.
By way of example, as shown in the 1977-1978 Irrigation Equipment Catalog published by Rain Bird Sprinkler Mfg. Corp. of Glendora, Calif., for a part circle Model 25 PJ sprinkler with a nozzle size of 1/8 inch, a minimum supply pressure of 35 pounds per square inch (psi) is required to achieve satisfactory water distribution and sprinkler operation. If the pressure is allowed to fall below this required level, the stream of water ejected from the nozzle of the sprinkler may not impart sufficient energy to the drive arm to properly drive the sprinkler in the forward and reverse directions. Moreover, a part circle impact drive sprinkler requires a higher supply pressure than a full circle sprinkler because, at each end of the preselected arc within which the part circle sprinkler operates, the sprinkler must be driven with sufficient energy not only to drive the sprinkler in the desired direction, but also to actuate the reversing mechanism of the sprinkler. Large amounts of energy are required to maintain the supply pressure necessary to effect satisfactory drive operation of the sprinkler in the forward and reverse directions.
This is particularly true in large agricultural applications, such as the well known pivot move type sprinkler systems, where it is often necessary to provide high capacity supply pumps typically run by natural gas or electricity, and often even booster pumps along the supply line in order to maintain the required pressure. The cost of the energy consumed by high capacity supply pumps, in addition to the booster pumps, significantly increases the cost of operating such sprinkler systems.
In addition, it is highly desirable for full or part circle impact drive sprinklers to be relatively compact in size. This is particularly true of sprinklers intended for pop-up operation within a generally cylindrical subterranean housing. In a pop-up application, a smaller sprinkler can be contained in a smaller housing thereby presenting a desirable less conspicuous appearance while requiring less material to produce, and therefore being relatively inexpensive to manufacture.
Accordingly, there exists a need for a convenient, effective and economical device which can be contained within a relatively inexpensive small housing, and which is capable of operating at energy saving low pressures. As will become apparent from the following, the present invention satisfies that need.